This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. A MRAC grant in the total amount of 1,344,000 SU time (1,152,000 SUs on Ranger and 192,000 SUs in roaming) is requested to run large-scale Molecular Dynamics (MD) simulations of Rhodopsin, Serotonin (5-HT2AR), and Dopamine (D2R) G-protein coupled receptors (GPCRs) in explicit lipid membrane environments. The proposed calculations will support achieving the specific aims of the Program Project Grant (PPG: 2 P01 DA012923-08, H. Weinstein, PI). The long-term goal of this project is to investigate the role of specific cholesterol-receptor interactions in GPCR functioning, stability, and oligomerization during cell signaling.